1. Field of the Invention
The present invention relates to filled unsaturated polyester resin compositions having lowered viscosities so as to be more processable.
2. Description of the Prior Art
Filled unsaturated polyester resin compositions are well-known commercial products for the manufacture of a variety of products for which either sheet metal or wood has traditionally been used. Some examples include auto bodies, wall panels, and boat hulls. It has been customary to add filler to the polyester resin compositions to reduce the cost of the finished product, to improve the surface appearance of the product, and to improve its water resistance. However, addition of the levels of filler needed to accomplish these results also increases the viscosity of the filled polyester composition rendering it more difficult to process. A number of prior art attempts have been made to decrease the viscosity of filled unsaturated polyester resin compositions by the use of additives.
U.S. Pat. No. 2,840,538 to H. F. Minter et al. advocates the use of: a melamine resin; a soap, such as tall oil; or a fatty acid, such as stearic acid, as coatings for the filler material.
Canadian Patent No. 766,764 advocates the use of a metal salt of an organic acid having from 3 to 18 carbon atoms as a viscosity reduction agent.
Japanese Kokai No. 75/70,493 advocates the use of polystyrene for viscosity reduction.
Kunststoffe 68(2), 62-64 (1978) mentions the testing of approximately one hundred substances as potential viscosity reduction aids in aluminum hydroxide-filled polyester resin systems. The majority of additives were judged to be ineffective for the intended result. Only a few additives were judged to be "fairly effective" including styrene, a surfactant (available as CEFAX-EMULGATOR), an ethoxylated alkylphenol (available as TINOVETIN NR), and triethyl phosphate.